efl: Make stable single-valued getters consistent.

Instead of a getter with an explicit return type, change it to be a
single-valued property.

The eolian C generator takes care of making this single value the actual
return value of the C function.

This also makes these properties able to be reflected on.

The stack properties returns just a pointer and not a new ref, so no
@move needed.

Beta properties will be handled in a future commit.

Depends on D10601

src/lib/ecore/efl_loop_timer.eo

@@ -26,7 +26,9 @@ class Efl.Loop_Timer extends Efl.Loop_Consumer
       @property time_pending {
          [[Pending time regarding a timer.]]
          get {
-            return: double; [[Pending time]]
+         }
+         values {
+            pending: double; [[Pending time]]
          }
       }
       timer_reset {

src/lib/efl/interfaces/efl_gfx_stack.eo

@@ -42,7 +42,9 @@ interface Efl.Gfx.Stack
 
            See also @.layer.]]
          get {
-            return: Efl.Gfx.Stack @no_unused; [[The @Efl.Gfx.Stack object directly below $obj, if any,
+         }
+         values {
+            below: Efl.Gfx.Stack; [[The @Efl.Gfx.Stack object directly below $obj, if any,
                                                 or $null, if none.]]
          }
       }
@@ -54,7 +56,9 @@ interface Efl.Gfx.Stack
 
            See also @.layer and @.below]]
          get {
-            return: Efl.Gfx.Stack @no_unused; [[The @Efl.Gfx.Stack object directly below $obj, if any,
+         }
+         values {
+            above: Efl.Gfx.Stack; [[The @Efl.Gfx.Stack object directly below $obj, if any,
                                                 or $null, if none.]]
          }
       }

src/lib/evas/canvas/efl_canvas_object.eo

@@ -352,7 +352,9 @@ abstract Efl.Canvas.Object extends Efl.Loop_Consumer implements Efl.Gfx.Entity,
            See also @.clipper.
          ]]
          get {
-            return: iterator<Efl.Canvas.Object> @no_unused; [[An iterator over the
+         }
+         values {
+            objects: iterator<Efl.Canvas.Object> @move; [[An iterator over the
                                              list of objects clipped by $obj.]]
          }
       }